Organic matter decomposition products

Water is modified by soil when added as either rain or irrigation [2], The modifiers are plants, plant roots, organic matter, organic matter decomposition products, carbon dioxide and other gases in the soil atmosphere, and dissolved inorganic compounds, commonly salts. Of particular importance is the change in pH that accompanies this modification of water. Thus, components obtained from soil by added extraction water will be significantly different from... 

Humus acids are soluble part of humus, i.e., dead organic matter decomposition products. Among humus acids can be distinguished humic acids proper (they are noticeably soluble only in alkali water) and fulvic acids (from Latin/m/vms for red, carroty), which are soluble in any water solutions. These humus acids in dry form are unsmeltable amorphous powdery matter. Fulvic acids are yellow to yellowish-brown, humus - dark-fulvous to black (Figure 3.20). In humid state they resemble clay in consistency. In water, they exist in suspended, colloidal and dissolved form. In their... 

Ueda S, Go CSU, Ishizuka S, Tsuruta H, Iswandi A, Murdiyarso D (2005) Isotopic assessment of C02 production through organic matter decomposition in the tropics. Nutr Cycling Agroecosys 71 109-116... 

Water quality changes in reservoirs (primary production, sedimentation, organic matter decomposition, oxygen consumption)... 

Early studies of acidified lakes often reported lower chlorophyll a and greater transparency. The resulting oligotrophication hypothesis (31) stated that lower rates of organic-matter decomposition and coverage of bottom sediments by mats of acidophilic algae or Sphagnum would reduce the circulation of nutrients and thence decrease primary productivity. Og-... 

The major N product of organic matter decomposition in seawater is NH4+, but NH4+ is present at trace or undetectable levels in the huge volume of the deep ocean. Rather, deep water contains NOs" at 20-40 pM concentrations, which would seem to imply that nitrification occurs mainly in the deep ocean. Nitrate concentrations in the surface ocean are usually maintained at low levels because phytoplankton assimilate N03 more rapidly than it can be suppHed by mixing or diffusion from the deep NOs" reservoir. Ammonium, which is produced in the photic zone by heterotrophic processes, is also usually immediately assimilated by phytoplankton and heterotrophic bacteria before it can be nitrified. The important physical and biological differences in the source functions of NH4+ and NOs" are... 

Urea ((NH2)2CO) is excreted by larger organisms, can be a product of bacterial organic matter decomposition, and is a highly labile form of N for plankton nutrition (Bronk, 2002). Reports of concentrations in oceanic waters are relatively scarce, but are quite low (<0.5 pM Antia et al, 1991). There are currently two methods commonly used to measure urea concentrations—the urease method (McCarthy, 1970) and the monoxime method (Mulvenna and Savidge, 1992 Price and Harrison, 1987). 

Hammond et al. (1996) used fits of the model of Equation (1) to pore-water O2 and NOJ profiles in the central equatorial Pacific to define the rate of organic matter oxidation as a function of depth below the sediment-water interface. Their model was built on a two-exponential description of the O2 consumption or NO production rate (Equation (2)). They assumed that the fraction of organic matter decomposition represented by the exponential with a short scale length was the highly reactive fraction, the fraction represented by the exponential with the longer scale length was a less reactive fraction, and that there was a third fraction that was unreactive on the... 

Many studies of the impact of chemical diagenesis on the carbonate chemistry of anoxic sediments have focused primarily on the fact that sulfate reduction results in the production of alkalinity, which can cause precipitation of carbonate minerals (see previous discussion). However, during the early stages of sulfate reduction (—2-35%), this reaction may not cause precipitation, but dissolution of carbonate minerals, because the impact of a lower pH is greater than that of increased alkalinity (Figure 4). Carbonate ion activity decreases rapidly as it is titrated by CO2 from organic matter decomposition leading to a decrease in pore-water saturation state. This process is evident in data for the Fe-poor, shallow-water carbonate sediments of Morse et al. (1985) from the Bahamas and has been confirmed in studies by Walter and Burton (1990), Walter et al. (1993), and Ku et al. (1999) for Florida Bay, Tribble (1990) in Checker Reef, Oahu, and Wollast and Mackenzie (unpublished data) for Bermuda sediments. 

The study has been broken into two parts the first concentrates on describing diagenetic processes involving organic-matter decomposition and production or consumption of the nutrients SO ", NH4, alkalinity, and HP04. The second emphasizes the associated chemical behavior of Fe and Mn (Part II). Several types of measurements were made (1) seasonal pore water and solid-phase analyses, (2) direct measurement of solute fluxes out of the sediment, (3) rates of reaction as a function of depth and temperature, and (4) the abundance and composition of the fauna at each station. Taken together, these measurements provide one of the most detailed descriptions of controls on diagenesis near the sediment-water interface that is presently available. 

A further mechanism that has yet to be considered is the role of macrofauna in the decomposition of organic matter. In the seasonally dry tropics, for example, it has been estimated that 20% of organic matter decomposition results from the action of termites (Holt and Coventry, 1990). Since methane is an abundant product of the decomposition of organic matter in termite nests, it is possible that the remaining SOC residue is sub.stantially enriched in " C. 

A narrower scientific definition (and the most commonly accepted one) would limit wetlands to areas in which there are plants. This type of wetland is usually much higher in soil organic matter than those without emergent plants. This is due to the high production of plant biomass and the slow rate of organic matter decomposition, because of the limited supply of oxygen in the wet soil. 

Compare and contrast aerobic and anaerobic organic matter decomposition in terms of energy yield, rate, microbial biomass, efficiency, and end products. 

In most freshwater wetlands and aquatic systems, sulfate concentrations are present at low concentrations to make them ineffective as electron acceptors to support organic matter decomposition. The suppression of methane production during Fe(HI) oxide reduction was demonstrated in laboratory experiments by Roden and Wetzel (1996) (Figure 10.34). In their study, methane was not produced until a major portion of the Fe(III) oxide was reduced, as evidenced by Fe(II) accumulation. Iron oxides are present in high concentrations in mineral wetland soils such as those... 

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